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102

Revision 1.1

SuperI/O Module (Continued)

4.7.10 ACB Registers

Each functional block is associated with a Logical Device

Number (LDN) (see Section 4.3.2 "Banked Logical Device

Registers" on page 68). ACCESS.Bus Port 1 is assigned

as LDN 05h and ACCESS.bus Port 2 as LDN 06h. In addi-

tion to the registers listed here, there are additional config-

uration registers listed in Section 4.4.2.4 "LDN 05h and 06h

- ACCESS.bus Ports 1 and 2" on page 78.

Table 4-29. ACB Register Map

Offset

Type

Name

Reset

Value

00h

R/W

ACBSDA. ACB Serial Data

xxh

01h

R/W

ACBST. ACB Status

00h

02h

R/W

ACBCST. ACB Control Status

00h

03h

R/W

ACBCTL1. ACB Control 1

00h

04h

R/W

ACBADDR. ACB Own Address

xxh

05h

R/W

ACBCTL2. ACB Control 2

00h

Table 4-30.

ACB Registers

Bit

Description

Offset 00h

ACB Serial Data Register - ACBSDA (R/W)

Reset Value: xxh

Width: Byte

7:0

ACB Serial Data. This shift register is used to transmit and receive data. The most significant bit is transmitted (received)

first, and the least significant bit is transmitted last. Reading or writing to ACBSDA is allowed only when ACBST[6] is set, or

for repeated starts after setting the ACBCTL1[0]. An attempt to access the register in other cases may produce unpredict-

able results.

Offset 01h

ACB Status Register - ACBST (R/W)

Reset Value: 00h

Width: Byte

This is a read register with a special clear. Some of its bits may be cleared by software, as described below. This register maintains the

current ACB status. On reset, and when the ACB is disabled, ACBST is cleared (00h).

SLVSTP (Slave Stop). (R/W1C) Writing 0 to SLVSTP is ignored.

0: Writing 1 or ACB disabled.

1: Stop Condition detected after a slave transfer in which ACBCST[2] or ACBCST[3] was set.

SDAST (SDA Status). (RO)

0: Reading from ACBSDA during a receive, or when writing to it during a transmit. When ACBCTL1[0] is set, reading ACB-

SDA does not clear SDAST. This enables ACB to send a repeated start in master receive mode.

1: SDA Data register awaiting data (transmit - master or slave) or holds data that should be read (receive - master or slave).

BER (Bus Error). (R/W1C) Writing 0 to this bit is ignored.

0: Writing 1 or ACB disabled.

1: Start or Stop Condition detected during data transfer (i.e., Start or Stop Condition during the transfer of bits [8:2] and

acknowledge cycle), or when an arbitration problem detected.

NEGACK (Negative Acknowledge). (R/W1C) Writing 0 to this bit is ignored.

0: Writing 1 or ACB disabled.

1: Transmission not acknowledged on the ninth clock (In this case, SDAST (bit 6) is not set).

STASTR (Stall After Start). (R/W1C) Writing 0 to this bit is ignored.

0: Writing 1 or ACB disabled.

1: Address sent successfully (i.e., a Start Condition sent without a bus error, or Negative Acknowledge), if ACBCTL1[7] is

set. This bit is ignored in slave mode. When STASTR is set, it stalls the ACCESS.bus by pulling down the ABC line, and

suspends any further action on the bus (e.g., receive of first byte in master receive mode). In addition, if ACBCTL1[1] is

set, it also causes the ACB to send an interrupt.

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